There are numerous prior art precipitation measurement systems available. As used in the present application, precipitation includes, but is not limited to, rain, mist, drizzle, fog, snow, freezing rain, freezing drizzle, sleet, and hail. Currently, there are various rain gauges and snow gauges known that are designed to quantify precipitation that reaches the earth's surface. Some prior art systems attempt to quantify the precipitation based on a measurable weight of precipitation that accumulates in a container. For example, a container can be provided to collect precipitation and upon accumulation of a predetermined amount, the container pours the precipitation into a weighing container. The weight of the collected sample can be converted into a total accumulation of precipitation.
A problem experienced with these types of systems is that the overall accuracy of the system is dependent upon the mechanical resolutions of accumulation. For example, light precipitation may go unnoticed by evaporating before a measurable amount accumulates.
In an attempt to overcome the various drawbacks of mechanical precipitation measurement systems, thermal plate precipitation measurement systems have been developed and are described in U.S. Pat. Nos. 5,744,711 and 6,546,353, which are hereby incorporated by reference. The thermal plate measurement systems use a pair of thermal plates that are kept at a substantially constant temperature. One of the thermal plates is exposed to precipitation while the other thermal plate is exposed to the same atmospheric temperature and wind, but is protected from precipitation. The difference in power used to maintain the individual thermal plates at the substantially constant temperature is quantified and converted into a precipitation rate.
FIG. 1 shows a prior art thermal plate precipitation measurement system 10. Similar prior art thermal plate precipitation measurement systems are shown and described in the '353 patent. The prior art thermal plate precipitation measurement system 10 includes a sensor electronics stand 11. The sensor electronics stand 11 includes a top thermal plate 12, a bottom thermal plate 13, a sensor controller 14, solar/infrared radiation sensor 16, a temperature sensor 17, and a remote processor 18. The top and bottom thermal plates 12, 13 are connected to a single mounting post 19 angled downward at approximately 30 degrees. The top thermal plate 12 is oriented generally horizontal relative to the earth's surface to permit maximum exposure to falling precipitation. In some cases, however, such as when the thermal plate precipitation measurement system 10 is positioned on an inclined surface, the top thermal plate 12 may be positioned at some angle to horizontal to maximize exposure to falling precipitation.
The bottom thermal plate 13 is positioned in a facial relationship directly under the top thermal plate 12. This orientation subjects the bottom thermal plate 13 to the same ambient temperature and/or airflow while facilitating a maximum protection from falling precipitation. The thermal plate precipitation measurement system 10 may further include an insulation layer 21. The insulation layer 21 may be positioned between the two thermal plates 12, 13 to prevent heat from one of the thermal plates 12, 13, from affecting the other one of the thermal plates 12, 13.
The top thermal plate 12 is further shown with concentric ridges 22, 23, 24. The concentric ridges 22, 23, 24 improve upon the thermal plate provided in the '711 patent and are provided to help catch and retain precipitation on top of the thermal plate 12. Therefore, the precipitation is prevented from flowing off the thermal plate 12 prior to evaporating. It should be appreciated that the bottom thermal plate 13 is substantially identical to the top thermal plate 12 so that the two thermal plates 12, 13 heat and cool in a linear relationship to each other.
The sensor electronics stand 11 is mounted on a post 25 that elevates the top and bottom thermal plates 12, 13 above the ground. The post 25 includes a base plate 26. The base plate 26 can support the mounting posts 19, 20 and orient the thermal plates 12, 13 in a desired direction.
The sensor controller 14 includes a processor that controls the temperature of the thermal plates 12, 13. The sensor controller 14 is in communication with the top and bottom thermal plates 12, 13, the solar/infrared radiation sensor 16, and the temperature sensor 17. The sensor controller 14 is shown in communication with the remote processor 18 via lead 30. The remote processor 18 can collect data from the sensor controller 14 for real-time or subsequent precipitation rate calculation and processing.
As taught by the '353 patent, the top and bottom thermal plates 12, 13 can be maintained at a substantially constant temperature by adjusting the power to the plates 12, 13. As precipitation falls on the top thermal plate 12, the energy required to maintain the temperature of the top thermal plate 12 increases as the precipitation melts and evaporates, thereby cooling the top thermal plate. Ideally, the thermal plates 12, 13 are maintained at a temperature that is below the local boiling point of water, yet hot enough to evaporate the water within a predetermined amount of time. The '353 patent teaches that the predetermined amount of time is ideally 5-10 seconds. As can be appreciated, the additional energy required to maintain the top thermal plate 12 at the predetermined temperature could be determined by the sensor controller 14. The additional energy is due to the latent heat of vaporization and therefore is proportional to the amount of precipitation falling on the top thermal plate 12. If the precipitation is snow or ice, for example, the energy increases by the latent heat of melting, also known as the latent heat of fusion. Consequently, the difference in power consumption of the top plate 12 versus the power consumption of the bottom plate 13 is proportional to the rate of precipitation falling on the top plate 12 and can easily be calculated by those having ordinary skill in the art as explained by the '711 and '353 patents.
FIG. 2 shows another prior art thermal plate precipitation measurement system 20, which is also disclosed in the '353 patent. The thermal plate precipitation measurement system 20 further includes a second thermal plate system 30. The second thermal plate system 30 is identical to the first thermal plate system 10; however, the second thermal plate system 30 is attached to the post 25 by an arm 35 to position the second thermal plate system 30 at a different elevation than the first thermal plate system 10. The '353 patent explains that it is essential to position the thermal plate systems at different elevations because the second thermal plate system 30 is provided to determine if the precipitation is new precipitation or precipitation that has already fallen to the ground and impacts the measurement system due to blowing winds. For example, if the two thermal plate systems 10 and 30 calculate the same amount of precipitation, the precipitation is new. Conversely, if the lower thermal plate system 30 calculates a greater amount of precipitation, then some of the precipitation calculated by the lower thermal plate system 30 is attributable to blowing snow that has already fallen. While the measurement system 20 makes some improvement over the measurement system 10, the measurement system 20 still suffers from noise problems. Further, the measurement system 20 is unable to adequately determine if the precipitation is rain or snow.
While the thermal plate systems described above improve upon the mechanical measurement systems, they still suffer from noise generated from short and long wave radiation, sustained updrafts/downdrafts over the plate, non-horizontal orientation of the thermal plates, etc. Consequently, the current thermal plate systems have a minimal detectable precipitation rate of 0.01 inches/hr (0.25 mm/hr) when the winds are less than 6.6 ft/s (2 m/s). However, with winds greater than 26 ft/s (8 m/s), the detectable precipitation rate increases to 0.04 inches/hr (1 mm/hr). Further, the thermal plate systems currently available have difficulty properly determining what type of precipitation is present. Therefore, there is a need in the art for an improved thermal plate precipitation measuring system.
The present invention overcomes these and other problems and an advance in the art is achieved. The present invention provides a thermal plate precipitation measuring system including two or more individual plate systems that are configured at two different temperatures. For example, one of the plate systems may be configured at a temperature sufficient to vaporize precipitation within a predetermined time while the second plate system may be configured at a lower temperature that can melt precipitation but does not vaporize the precipitation within the predetermined time.